1. Field of the Invention
The present invention relates to a double pipe and a method of manufacturing the same.
2. Description of Related Art
Piping for circulating, for example, coolant employs, among others, a double pipe composed of an outer pipe and an inner pipe arranged in the outer pipe to form dual passages.
Employing the double pipe makes a piping layout simpler and more compact, and therefore, is advantageous for a piping layout with many restrictions. In particular, a double pipe is highly advantageous for a vehicle air conditioner where a piping layout is greatly limited due to vehicle structure. Employing the double pipe is also advantageous in simplifying air-conditioner assembling work and reducing manufacturing cost.
A conventional double pipe is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2001-341027 that arranges connecting ribs between an outer pipe and an inner pipe of the double pipe. The double pipe with the connecting ribs is usually produced by extruding or drawing an aluminum material through dies.
The extruding or drawing process to form the double pipe having the connecting ribs requires complicated metal dies. In addition, the double pipe with the connecting ribs involves a cutting process of the connecting ribs when terminating ends of the double pipe. These necessities increase the manufacturing cost of the double pipe.